Gilead's decision to price Sovaldi at $84,000 per treatment may open door for competitors like Abbvie to gain market share from cost-conscious pharmacy benefits managers.

The top medical officer for pharmacy benefits manager Express Scripts ( ESRX) expressed concerns about high pricing for the new crop of hepatitis C pills, most notably Gilead Sciences' ( GILD) Sovaldi, according to a Bloomberg story Tuesday.

Solvadi may be pitted against other hepatitis C therapies, Express Scripts' chief medical officer said, and "tough formulary decisions" will be made.

Shares of Gilead are down 4.5% to $71.84 after the Bloomberg story hit the wires. Shares of Abbvie, on the other hand, are up 4.5% to $53.51.